Compacted hydrazine bisborane fuel and method of operating gas generators



double base compositions.

United States Patent O COMPACTEI) HZDRAZINE BISBORANE FUEL AND METHOD OF OPERATING GAS GENERATORS David C. Sayles, Huntsville, Ala, assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Apr. 23,1963, Ser. No. 275,168 9 Claims. (Cl. 6035.4) (Granted under Title 35, US. Code (1952), sec. 266) source on board the rocket propelled device itself to operate various components in the guidance and aerodynamic control systems While in flight. One such power source is small turbines driven by the exhaust gases generated from a burning solid propellant composition. The exhaust gases are directed toward the turbine blades causing the turbine to rotate. The turbines operate small generators, pumps, and the like to provide the rocket with energy for operating guidance and fuel controls.

A propellant useful for driving these small turbines should be relatively slow burning and should produce as little heat as possible during combustion. There are only a few solid propellant compositions that lend themselves for gas generator application, and these are of two types: ammonium nitrate composite propellants and Powdered aluminum is occasionally incorporated as a fuel or combustion stabilizer in these compositions. V

While these previously used'compositions are acceptable for many applications, it has been found that their use in rockets whose guidance depends on the transmission of infrared signals leads to interference inthe signal transmission with a corresponding loss in the effective range and accuracy of the rocket. This is particu larly true in military rockets such as antitank weapons whose flight is observed through infrared tracking means with any necessary corrections in the rockets flight being made through electrical or radio signals transmitted to instruments on board the-rocket.

The conventional gas generating compositions interfere with the infrared signal because of the large particles in the exhaust plume from the burning composition. Water vapor particularly interferes with the signaltranssion as does aluminum oxide particles when aluminum is a fuel component. However, any particles larger than about to 10 microns interferes with the signal and should be eliminated if possible. 7

It has now been determined that the use of hydrazine bisborane or compositions consisting essentially of hydrazine bisborane and a binder overcome the disadvantages of the conventional gas generating compositions. Once, hydrazine bisborane is brought to its decomposition temperature it decomposes with the evolution of sufficient heat to sustain its complete decomposition. The heat evolved from the decomposition is not of such quantity as to present a problem of cooling. The exhaust is completely free. from water and is composed predominantly of only boron nitride and hydrogen. The boron nitride particles average in size from two to three microns. The exhaust plume from the decomposition of hydrazine bisborane offers little interference to the transmission of infrared signals. Moreover, conventional mechanical filters can remove the boron nitride particles, if necessary, leaving only hydrogen as an exhaust component. An exhaust of hydrogen offers only negligible interference to the transmission of the infrared signal.

In accordance with the foregoing, it is an object of the present invention to provide improved gas generating compositions.

A further object of the invention is to provide an improved gas generating composition the exhaust plume of which does not interfere with the transmission of infrared signals.

The manner in which these and other objects are to be accomplished will become. apparent from the detailed description set forth hereinafter.

. Hydrazine bisborane, or hydrazine diborane as it is sometimes referred to in the literature,'is the 1:1 adduct of diborane and hydrazine and can be represented by the structural formula BH -NH NH -BH It is 'a white crystalline solid which can be purchased commercially. One method of preparation consists of reacting diborane with hydrazine in an ethereal solutionat -80 C.

When hydrazine bisborane is heated to a temperature of 1000 C. it decomposes according to the following formula: NHZNHZ EH39 5H2+2B3N3.

Thus, it is seen that the decomposition of hydrazine bisborane is characterized by the evolution of a considerable amount of gaseous materials which are waterfree. Mechanical filtering of the boron nitride leaves only gaseous hydrogen in an exhaust plume. Typical mechanical filters for removal of the boron nitride. are the sintered glass filters which find widespread usage in industry. 7

Unless the optimum is desired in theremoval of transmission interference, it is'not necessary to filter the boron nitrideparticles. In those instances where the transmission signals is of no concern, it is preferable not to filter born nitride since greater thrust for driving the turbine is thereby achieved.

No alteration in conventional gas generating appaent invention'is 'tosubstitute hydrazine bisborane for the presently used propellant composition. In one aspect of the invention'hydrazine bisborane is press-loaded into the fuel chamber of the gas generator hardware using a pressure plate which has a forward projecting cylindrical rod. In this manner a single cylindrical internal perforation can be produced in the gas generating charge. Of course, a star-shaped internal .perforation, or internal perforations of any other desired configuration can be produced by utilizing the proper shaped forward extending projections on the pressure plate in lieu of a single cylindrical rod. Moreover, the generator will function satisfactorily without any internal perforation. Compaction pressures of 10,000 to 20,000

pounds per square inch are adequate to form the gas Patented Feb. 23, 1965 =3 igniter presently used to fire the propellants of conventionally fueled gas generators can be used to initiate the hydrazine bisborane decomposition. Squibs and hot wires are examples of acceptable firing means.

Another means by which hydrazine bisborane can be employed is to incorporate with thorough mixing from about to by weight of an uncured liquid polymer into the hydrazine bisborane. If less than 5% by weight of liquid polymer is employed, the composition of hydrazine bisborane and polymer should be pressloaded into the hardware as described above. After the polymer cures, the physical properties of the grain have been altered so that the grain is stronger and more resistant to cracking than a grain lacking the polymeric binder. When 5% to 15% by weight of a liquid polymer is incorporated into the hydrazine bisborane, the composition may be sufliciently fluid to pour. If this is the case, the composition is poured into a suitable mold or the fuel chamber itself and allowed to cure into a solid grain. If the composition is not suficiently fluid for pouring, press-loading procedures are again necessary.

The incorporation of the polymeric binder docs improve the physical properties of the grain. However, since the polymeric material may function as a fuel and oxidizer as well as a binder, it is apparent that the burning of the binder will affect the particle size and con tent of the exhaust plume. Therefore, when feasible, it is preferable that as little binder as practical be employed if reduction of infrared transmission interference is the major objective and in such instances the binder should not exceed about 15% by weight of the composition.

Any of the conventional organic polymeric binders for solid fuels can be employed as the binder for hydrazine bisborane. Nylon, epoxy resins, liquid polysulfides such as LP-33 and the copolymers of butadiene and acrylic acid are particularly useful binders. It is apparent that a curing agent and accelerator may be necessary to achieve curing of the liquidpolymer as for example, amine curing agents for epoxy resins. However, the preparation of polymeric binders is well established and the manner in which a particular binder can be utilized with hydrazine bisborane will be obvious to those skilled in the art.

The following example is given to illustrate the preparation of a propellant charge containing a copolymer of butadiene and acrylic acid as the polymeric binder. In this particular example, the liquid copolymer was a commercially available product produced from a ratio of 80 parts by weight butadiene to parts by weight acrylic acid.

Example 1 A gas generating composition comprising about 92% by weight hydrazine bisborane and about 8% by Weight of a polymeric binder is made in the following manner. All proportions are set forth in parts by weight unless otherwise specified.

Eighteen grams of the liquid binder is prepared by mixing in a sigma blade mixer at room temperature 85 parts of the liquid polybutadiene-acrylic acid copolymer with 3.75 parts of the diglycidyl ether of glycerol and 11.25 parts by weight of BR18795, the trade designation of a commercially available epoxy curing agent which is the reaction product of epichlorohydrin and bis-phenol A. The curing agent has a probable structure corresponding to the formula or the dimer or trimer thereof or a mixture of all three. To this mixture is added with continued stirring 200 grams of hydrazine bisborane. Mixing is continued for about minutes at 38 C. to 42 C. during which time the viscosity of the binder increases due to the reaction of the diglycidyl ether with the carboxy groups of the polymer. The mixture is then deaerated in a deaeration hopper if desired or the deaeration step can be omitted and the mixture transferred directly to the fuel chamber of the gas generating device. The mixture is firmly packed in the chamber and then the loaded chamber is placed in an oven at about 78 C. to 82 C. for curing. At about C. the epoxy curing agent begins to react with carooxy groups in the polymer chain to produce crosslinking and thus solidify the mass. After about 48 hours the cure is complete and the loaded fuel chamber is ready for attachment to any conventional gas generating device.

In the above example, any other liquid diene-unsaturated acid copolymer can be substituted for the butadieneacrylic acid copolymer. Examples of some other polymers are the copolymers of butadiene and methacrylic acid, isoprene and acrylic acid, and isoprene and methacrylic acid. Furthermore, the ratio of diene to unsaturated carboxylic acid can vary widely and is not limited to the 80:20 ratio of Example 1. Ratios of :10, 85:15, and 70:30 are also satisfactory as are other ratios within this range. Moreover, as previously mentioned entirely different polymeric binders such as the polyurethane, the epoxide, nylon, and the polysulfides can also be utilized.

When the mixture is placed in the fuel chamber, it can be press-loaded even though a polymeric binder is present to insure complete filling of the chamber and close packing around any mandrel placed in the chamber. Pressures of 8000 p.s.i. to 10,000 p.s.i. are adequate for loading mixer containing at least 5% by weight of a polymeric binder. If less than 5% by weight is present, pressures of 10,000 p.s.i. to 20,000 p.s.i. should be utilized.

Tests with the gas generating compositions of the invention indicate a reduction of 60% to 80% in infrared transmission interference when compacted hydrazine bisborane alone is used as a fuel and boron nitride is filtered from the exhaust; 50% to 70% reductions when boron nitride is not filtered from the exhaust; and 40% to 70% reduction with the hydrazine bisborane composition containing a polymeric binder.

The above detailed description is for the purpose of illustration only and no undue limitation should be attributed to the invention as a result of this description except as reflected in the appended claims.

I claim:

1. A composition comprising a cured intimate mixture of about 85% to by Weight hydrazine bisborane and about 5% to 15% by weight of an organic polymeric binder.

2. A composition according to claim 1 wherein said organic polymeric binder is a member selected from the group consisting of polybutadiene-acrylic acid copolymers, polyurethanes, epoxy resins, and nylon.

3. A composition according to claim 1 wherein said organic polymeric binder is a copolymer of butadiene and acrylic acid.

4. A composition comprising a cured intimate mixture of about 92% by Weight hydrazine bisborane and about 8% by weight of the cured copolymer of polybutadiene and acrylic acid.

5. The method of operating a gas generator whereby large quantities of gases are produced, said method comprising elevating the temperature of compacted hydrazine bisborane to the decomposition temperature of said hydrazine bisborane.

6. The method of operating a gas generator whereby large quantities of gases are produced, said method comprising elevating the temperature of a composition consisting essentially of a cured intimate admixture of about 85% to about 95% by weight hydrazine bisborane and about 5% to about 15% by weight of an organic polymeric binder.

3,170,283 5 6 7. The method according to claim 6 wherein said References Cited by the Examiner binder is selected from the group consisting of poly- UNITED STATES PATENTS butadiene-ac lic acid co 0 mers, o1 urethanes, e ox resins 3 p p y P y 3,099,629 7/63 Henbusch 149-36 X 8. The method according to claim 6 wherein said binder is a copolymer of butadiene and acrylic acid.

9. The method according to claim 7 wherein said composition consists essentially of a cured intimate admixture of about 92% by weight hydrazine bisborane and about 8% by weight of a copolymer of polybutadiene and 10 CARL QUARFORTH Pnmary Exammer' acrylic acid. I REUBEN EPSTEIN, Examiner.

5 OTHER REFERENCES Steindler et al.: American Chemical Society Journal, vol. 75, N0. 1, Feb. 3, 1953, p. 756. 

5. THE METHOD OF OPERATING A GAS GENERATOR WHEREBY LARGE QUANTITIES OF GASES ARE PRODUCED, SAID METHOD COMPRISING ELEVATING THE TEMPERATURE OF COMPACTED HYDRAZINE BISBORANE TO THE DECOMPOSITION TEMPERATURE OF SAID HYDRAZINE BISBORANE.
 6. THE METHOD OF OPERATING A GAS GENERATOR WHEREBY LARGE QUANTITIES OF GASES ARE PRODUCED, SAID METHOD COMPRISING ELEVATING THE TEMPERATURE OF A COMPOSITION CONSISTING ESSENTIALLY OF A CURED INTIMATE ADMIXTURE OF ABOUT 85% TO ABOUT 95% BY WEIGHT HYDRAZINE BISBORANE AND ABOUT 5% TO ABOUT 15% BY WEIGHT OF AN ORGANIC POLYMERIC BINDER. 